The set is located on a dead body beneath a bridge in Ordina, Liturgical Town, but the tricky part to locate the town is locating it on the map Elden Ring Runes. Ordina is situated in the topmost portion of the consecrated Snowfield and is a secret zone located above those of Mountaintops of the Giants, and is only unlockable through finding both halves the Haligtree Secret Medallion.
The right half of the Secret Medallion is in the Village of the Albinaurics in Liurnia and the left half is left by Commander Niall in Castle Sol, which itself is situated within The Mountaintops of the Giants.
After both halves have been secured, you'll be able to return in the Grand Lift of Rold and present the Haligtree Secret Medallion to the statues. This will open the Consecrated Snowfield zone and, to an extent, Ordina, where you'll discover the Black Knife armor and complete your build.
The Green Turtle Talisman enhances recovery speed. It's located at the beginning of the game, within Summonwater Village, which is located in the eastern part of Limgrave buy Elden Ring weapons. Summonwater is situated directly in middle of the one land route that links Limgrave and Caelid It is also the site of the location of a Tibia Mariner battle.